1. Field of the Invention
The present invention relates to a bicycle power meter, and more particularly to a dynamometer to determine rider applied torque, and to calculate and display the horsepower developed.
2. Description of the Prior Art
Bicyclists as a class, and particularly competitive riders, are interested in their level of performance. Numerous devices exist for determining the speed of the bicycle, distance traveled, pulse rate of the rider, etc. However, an easy and precise means for determining the power output of a bicycle rider is not available. Display of the power output in watts or calories would enable a rider to assess his performance under a variety of conditions. It would be an important and continuing indication of the level of performance, unaffected by the rider's subjective perception. A bicyclist approaching the limit of his physical stamina may perceive his level of physical exertion to be greater than it actually is, and an effective power meter would immediately indicate whether or not his perception was correct.
In the case of a bicycle racer participating in a 100 mile race, an increase of only one percent in efficiency will result in a time advantage in excess of two minutes, which is almost a half mile advantage at the speeds common in such a race. A power meter would also enable an expert bicyclist to pace himself more accurately. By accurately measuring rider applied torque, such a power meter can not only calculate developed horsepower, but other related matters as well, such as the efficiency with which the power is applied by the rider to achieve bicycle speed.
Measurement of bicycle driving torque has been accomplished heretofore in a number of ways. Systems utilized strain gauges, which were sometimes associated with the pedals, sometimes with the crank arm, and sometimes with the chain wheel. Other systems measured torque by measuring drive chain tension. For various reason none of these has been particularly successful, some because they were contact systems which undesirably tapped part of the input energy to derive a so-called total power output. Ideally, torque should be measured in a contactless, frictionless indirect fashion.
Noncontact systems are known in the broad field of dynamometers, as represented by U.S. Pat. No. 4,520,681, issued June 4, 1985 to J. D. Moore et al. In that system the torque present in a rotating shaft was determined by sensing the relative angular positions of a pair of disks mounted on the shaft in axially spaced apart relation. In U.S. Pat. No. 2,616,290, issued Nov. 4, 1952 to C. R. Moore, a pair of sine wave generators were connected to the prime mover and to the load, respectively, and coupled together by torsion means. The level of torsion was then represented by the change in phase of the voltages generated by the sine wave generators. In U.S. Pat. No. 3,824,848, issued July 23, 1974 to J. R. Parkinson, a phase displacement torque measuring apparatus utilized a pair of toothed exciter wheels coupled to the shaft in spaced apart relation. The change in their relative angular position on the shaft indicated the torque developed in the shaft.
None of these references suggests any advantage which would be gained by employing a noncontact form of dynamometer in a bicycle, and they particularly lack any hint of how any such dynamometer could be redesigned or modified for use in determining the power output of a bicycle rider.